The invention concerns a three-phase brushless dc motor with a permanent-magnet rotor magnet arrangement having at least two pole pairs and a star-connected, three-phase stator winding, the winding's phases being arranged non-overlapping in slots of a slotted stator, with their currents being controlled via at least three semiconductor elements by at least three magnetic-field-sensitive position sensors, the latter in turn being controlled by the rotor magnet arrangement.
With motors controlled in this manner, especially in the case of motors operating at high power, there arises the problem of the field from the stator winding influencing the magnetic-field-sensitive position sensors although in theory, of course, these sensors should be responsive only to the rotor magnet poles. As a result of such influence, the commutation time points are in undesirable fashion shifted from their predetermined optimal times of occurrence. This is because any part of the stator-winding field that happens to be incident upon one of the rotor-position sensors is wrongly interpreted by the latter as part of the flux coming from a rotor-magnet pole. Accordingly, this problem becomes more severe, the higher the winding's current.